Transmutation of nuclear waste in accelerator-driven systems

Today more than ever energy is not only a cornerstone of human development, but also a key to the environmental sustainability of economic activity. In this context, the role of nuclear power may be emphasized in the years to come. Nevertheless, the problems of nuclear waste, safety and proliferation still remain to be solved. It is believed that the use of accelerator-driven systems (ADSs) for nuclear waste transmutation and energy production would address these problems in a simple, clean and economically viable, and therefore sustainable, manner. This thesis covers the major nuclear physics aspects of ADSs, in particular the spallation process and the core neutronics specific to this type of systems. The need for accurate nuclear data is described, together with a detailed analysis of the specific isotopes and energy ranges in which this data needs to be improved and the impact of their uncertainty. Preliminary experimental results for some of these isotopes, produced by the Neutron Time-of-Flight (n_TOF) experiment at CERN, are also presented. The detailed design analysis of the TRIGA Accelerator-Driven Experiment (TRADE), the first ADS experiment at real power, is presented together with the time evolution of the system and some investigations which validate the concept of transmutation in ADSs. A further design of the Energy Amplifier Demonstrator Facility (EADF), an 80 MWth leadbismuth cooled subcritical device, is presented, where the intrinsic advantages of the use of fast neutrons and the safety features of the device are demonstrated, using a state-of-the-art Monte Carlo burn-up code (EA-MC). Finally, Several high-level waste transmutation strategies are assessed. These include thorium-based systems to transmute waste transuranics and long-lived fission fragments, as well as the double strata approach, where plutonium is eliminated through the use of mixed oxide fuel (MOX) and the accumulated minor actinides (MAs) are eliminated in MA burners. Transmutation of Nuclear Waste in Accelerator-Driven Systems The conclusion of this research recapitulates the key features found in the design of both ADS experimental facilities and indicates their impact on nuclear waste transmutation. The safety features of the proposed ADS are summarised, together with design limitations due to the lack of accurate nuclear data. Finally, a possible nuclear waste transmutation scenario is proposed with an intermediate step, which includes the development of MA burners, progressively shifting nuclear power towards the more acceptable thorium fuel cycle.